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Season glints modeling for stabilized GEO satellites

Keywords:

E.A. Trushkova - Dr.Sc. (Phys.-Math.), Team Leader, JSC «RPC «PSI» (Moscow)
E-mail: katerinatr@mail.ru
V.S. Yurasov - Ph.D. (Eng.), Head of Department, JSC «RPC «PSI» (Moscow)
E-mail: vyurasov@mail.ru


Optical observations of geostationary space objects are the main source of information for their cataloging and tracking. The conditions for observing the same GEO satellite may differ greatly during different observation sessions. Therefore, it is used usually the reduced values for brightness, obtained as a result of recalculation of the brightness measurements to the same phase angles and range. The average value and the mean square error of the reduced brightness for many GEO satellites are quite informative characteristics of the reflective properties of space objects.
There is a significant number of operational triaxially stabilized spacecraft equipped with huge solar panels in GEO. On certain spatial-temporal conditions, these panels mirror the sunlight in the direction of the observer. This leads to an increase in the integral brightness of the satellite by several stellar magnitudes. These significant glints are seasonal in their nature. The analysis of the accumulated measurements shows that the specified character of the brightness behavior is typical for functioning satellites with large solar panels.
In this paper the analytic expressions for calculation the time and phase angle values are obtained, at which the specular reflection of sunlight can be observed. The phase angle value and the specular reflection time are uniquely calculated for the given latitude of the observation point and the difference between the longitude of the observation post and the GEO satellite.
In this paper analytic expressions for the calculation of time and phase angle values are obtained, at which peak gloss values appear under mirror reflection of sunlight. The values of the phase angle and the specular reflection time are calculated unambiguously for the given observer’s latitude and the difference between the longitude of the observer and GEO satellite.
For an arbitrary pair of Satellite-Observer, a computational algorithm is proposed for the search for a time moment when the angle between the direction of sunlight after reflection from the solar panels of the GEO satellite and the direction from the satellite to the observer is minimal.
In actual practice, a sharp increase of the brightness can be observed during a certain time interval near the calculated interval located in spring and autumn equinoxes. It is due to the presence of displacements in the direction of the solar panels, and also due to the presence of the effect of reflected light dispersion.
The obtained results were successfully used for correction the measured brightness values near the conditions of specular reflection on real data, which makes it possible, in particular, to correlate more effectively the obtained angular measurements, and also to detect emergency conditions in the stabilization of operational satellites.
The main parameters of the presented empirical model of the correction to the value of the reduced brightness are quite easily calculated annually for each individual pair of Observer-Satellite. The correction model was tested on real mea-surements and showed effective performance for 86% of triaxially stabilized GEO satellites.

References:
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